On the interference of J(HH) modulation in HSQMBC‐IPAP and HMBC‐IPAP experiments

The effects of phase modulation due to homonuclear proton–proton coupling constants in HSQMBC‐IPAP and HMBC‐IPAP experiments are experimentally evaluated. We show that accurate values of small proton–carbon coupling constants, ⁿJ_CH, can be extracted even for phase‐distorted cross‐peaks obtained from a selHSQMBC experiment applied simultaneously on two mutually J‐coupled protons. On the other hand, an assessment of the reliability of ⁿJ_CH measurement from distorted cross‐peaks obtained in broadband IPAP versions of equivalent HMBC and HSQMBC experiments is also presented. Finally, we show that HMBC‐COSY experiments could be an excellent complement to HMBC for the measurement of small ⁿJ_CH values. Copyright © 2013 John Wiley & Sons, Ltd.